The present embodiments relate generally to microphone networks. In particular, the location of microphones and filter responses to use for maintaining signal from a target while reducing influence from interference sources is determined.
There has been extensive work in the sensor placement problem using a variety of strategies. In design or selection of already implemented microphone arrays, the position of the selected microphones is solved using various approaches. Simulated annealing may be used to simultaneously optimize both weights and sensor locations on a linear array. Sensor location may be found using convex optimization. A binary variable of a sensor being off, 0, or on, 1, is relaxed by letting the variable instead be in the range of [0, 1]. In another relaxation, the unknown vector is converted to a matrix of 0s and 1s that belong to the class of Steifel matrices. The relaxation is to a 1-d sphere, and multiple dimensions are found using a greedy algorithm. Objective criteria are optimized using the KullbackLeibler divergence.
There has also been extensive work in the optimization of filterbanks. For example, a quadrature mirror filterbank is optimized to meet a user-given frequency response criteria. The ripple energy and out of band energy are minimized using a search algorithm whose success is highly dependent on both the starting point and step size. In another example, analysis filters at the microphones are fixed, and the synthesis filters prior to summation are optimized to achieve the best possible reconstruction given a user-specified integer time delay. The problem is converted to a H1 problem to take advantage of existing software. In yet another example, a multi-dimensional perfect reconstruction filterbank has both the analysis and synthesis filter as FIR filters of equal length. This non-linear and non-convex constraint is embedded directly into the optimization where the objective function measures the difference between a desired analysis filterbank and the optimized analysis filterbank.
With both placement and filter response criteria, it may be difficult or time consuming to determine microphone placement as well as filter response while still meeting the criteria of both decisions.